Watching as current increases to the electron beam at the Dual Axis Radiographic Hydrodynamic Test facility are members of the team that met a major performance milestone at the facility. Standing, left to right, are Orlando Abeyta of Machine Science Technology (DX-6), Kurt Neilsen (partly hidden) of Accelerator Construction (DX-8), Carl Ekdahl of DX-6, Jim Harrison, DX-8 and Vernon Smith both of DX-8. Seated are Pedro Valdez and Kevin Esquibel, both of DX-6. Photo courtesy of DARHT

DARHT meets technical milestone

A major tool of the nation's stockpile stewardship program has passed another test with flying colors.

The second axis of Los Alamos' Dual Axis Radiographic Hydrotest facility at Technical Area 15 achieved a key technical milestone on July 2, nine days ahead of schedule, said DARHT project director Rollin Whitman.

The DARHT project team generated and transported an electron beam from the injector of the second axis that exceeded 2.6 million electron volts and more than 300 amperes. Later that night, the team succeeded in increasing the current to 900 amperes, which is more than three times the beam current required to meet the initial milestone.

"This was really the first time we ran the electron beam at high current," Whitman explained. "It provides the first empirical evidence that we have an excellent design for the second axis injector. We had been running the machine for a few weeks and had a lot of confidence in the design, but before today we didn't know for certain."

DARHT, when fully operational in mid-2004, will provide time-resolved, three-dimensional radiographs of non-nuclear mock-ups of nuclear weapons primaries at the moment of implosion. This is done by producing X-rays with a pair of electron beam accelerators set at right angles to one another.

DARHT's first axis began producing single, two-dimensional images in the fall of 2000 and produced high-quality radiographs of four major hydrodynamic experiments in the summer of 2001. The second axis is designed to capture four images in succession over two microseconds, providing one three-dimensional radiograph and three other two-dimensional time-sequenced X-rays that will be used to validate the computer codes needed for continued certification of stockpile weapons.

In the weeks leading up to the event, the team gradually increased the charge to the injector column from one megavolt to 2.6 megavolts, conditioning the column with more than 200 pulses. Then they provided about 30 additional pulses to the electron beam cathode, after heating the cathode to about 1,100 degrees Celsius, to condition the cathode so it could drive the electron beam.

"When you are starting a new machine like this it's similar to breaking in a sophisticated sports car," Whitman said. "You need to engage each gear very carefully and check out all the operating conditions at every speed before you can run the car at full speed or, in our case, operate at full capacity and make X-rays."

The success of the second axis, which incorporates complex, innovative technology, shows the benefit of the strong design collaboration among Los Alamos, Lawrence Livermore and Lawrence Berkeley national laboratories, Whitman said.

For the next two months, the DARHT team will continue to take electron beam measurements and characterize the injector. The next major milestone is completing the installation of the second axis and running beam through the accelerator by the end of 2002. The first X-rays of hydrodynamic experiments using both axes are scheduled for approximately June 2004.

A recent aerial view of the Dual Axis Radiographic Hydrodynamic Test facility shows the two accelerators, set at right angles to each other, that will produce three-dimensional X-rays of hydrodynamic experiments.

-- Jim Danneskiold

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